Modern motor vehicles usually already have safety systems which, in driving situations in which a collision could occur with an object in the surroundings, actuate safety means which alert the driver to the danger and which can perform interventions into the driving behavior of the vehicle in order to avoid collisions and/or which increase the passive safety, i.e. reduce possible consequences of an accident for the vehicle occupants. A basis for actuating the safety systems is to sense the current driving situation by means of a suitable surroundings sensor system and to perform electronic evaluation of the acquired data with respect to the danger of collisions between the vehicle and the sensed objects. In this context, there is often the problem of the driving situation not being correctly analyzed on the basis of the acquired data relating to the object located in the surroundings of the vehicle. As a result incorrect triggering of the safety means can occur, and this can lead to an adverse effect on the driving comfort and, as for example in the case of an unnecessary braking process, can adversely affect the driving safety.
Sensors which are present in the motor vehicle are used to detect a direction of travel of a motor vehicle in order to avoid additional costs. Safety systems, such as driving stability control systems and vehicle occupant protection systems, for a motor vehicle having at least four wheels have a sensor which generates a yaw rate signal, a sensor which generates a lateral acceleration signal, a sensor which generates a steering angle signal, wheel speed sensors which generate rotational movement signals of the wheels, and a sensor which generates a longitudinal acceleration signal, which can be connected to an anti-lock brake control system and a traction control system and a yaw moment control system, an airbag system or a seat belt system. The seat belt devices can act on the wheel brakes of the brake system and/or the steering system of the motor vehicle.
Most wheel speed sensors which are used in series production today only supply information about the absolute value of the wheel speed, from which it is not possible to derive a direction of travel. Wheel speed sensors with which a direction of rotation can be detected are known but they are seldom used in series-production vehicles owing to the additional costs.
However, since the information on the direction of travel is very important for driving stability control systems or driver assistance systems, said information is generated from other existing variables.
For example, an intervention by the yaw moment control system during reverse travel must be avoided in order to prevent incorrect triggering of the actuators. The detection of reverse travel in the yaw moment control system (ESP systems) is carried out exclusively during cornering since during straight-ahead travel the yaw angle rate ψ hardly differs from zero and therefore a control intervention must not be performed. Reverse travel is detected by comparing the measured yaw angle rate ψmeas with a setpoint yaw angle rate ψsetp which is detected in a vehicle model. If the signs are opposed, and this also applies to the derivatives of the two variables over time, the yaw accelerations, the vehicle is in a bend through which it is traveling in reverse. In addition to the yaw angle rate, the variables of the lateral acceleration sensor and of the steering angle sensor are also included here in the detection of reverse travel (DE 195 15 048 A1).
Detection of reverse travel is also necessary in order to avoid incorrect control operations for a preventive protection system which avoids accidents, has the purpose of performing early detection of motor vehicle collisions and uses a surroundings sensor system. Preventive protection systems by means of which accidents are avoided and the consequences of accidents are reduced generally carry out the following basic steps in this context:
a) detection of an object in front of the vehicle in the direction of the vehicle,
b) detection of possible contact between the vehicle and the object as a function of the relative position with respect to one another,
c) preparation or triggering of a driver-independent braking or steering process as a function of the result of the detection or of possible contact with the object.
In this context, for example a driver-independent, automatic braking intervention or a reduction in the absolute value of the vehicle speed when an object is approaching from the front during reverse travel is counter-productive. Such a situation may occur, for example, if a motor vehicle is traveling in reverse downhill while a vehicle is approaching it from the front at a relatively high speed.
This situation cannot be prevented by the above-described detection of reverse travel with a yaw moment control system since cornering of the motor vehicle is a precondition for detection of reverse travel. The described incorrect triggering can, however, also easily occur during reverse travel with a preventive protection system for the early detection of motor vehicle collisions.
The detection is provided for a motor vehicle with a preventive protection system which avoids accidents and which comprises a plurality of safety devices, in particular also driving stability devices and vehicle occupant protection devices, and in which the safety and vehicle occupant protection devices can be actuated by at least one surroundings sensor system which detects the surroundings of the vehicle and has the purpose of performing the early detection of motor vehicle collisions. Radar sensors and/or infrared sensors as well as camera systems can be used individually or in combination as sensors for sensing the surroundings.